Three-dimensional fabric covers for seats have in the past been produced from woven or knitted fabric which has been cut into shaped panels which are then sewn together.
More recently, it has been found possible to continuously knit one-piece three-dimensional upholstery fabric covers, which removes the need for cutting and sewing, and has the desired shape to serve as covers for the back and base cushions of motor vehicle seats; see, for example, U.S. Pat. Nos. 5,308,141 and 5,326,150.
It is necessary to provide anchorage devices at the edges of the covers to enable the covers to be secured to a support and held tautly over their respective cushions. The anchorage devices typically take the form of tubular portions or flaps which may be formed by sewing or by integrally knitting said portions. The tubular portions accommodate rods which are recessed into the cushions and secured under the support. If the base and back cushions comprise bolsters, it may also be necessary to provide anchorage devices on the undersurface of the cover in order to conform the cover to the shape of the upper surface of the cushion. The anchorage devices are typically open-ended tubular flaps which are formed by sewing or integral knitting as shown in U.S. Pat. Nos. 5,308,141 and 5,326,150. In some applications, metal rods are inserted into the tubular flaps, and the metal rod and flap are secured to the seat frame by hog rings which pass around the metal rod. Typically the tubular flap may have apertures therein to allow access for the hog rings. In other cases, the hog rings may pass through the fabric of the flap.
For continuously knitted 3-D covers, the provision of apertures in the flaps is a relatively slow operation, but if such apertures are not provided the operator may inaccurately position the hog ring so that tensions in the taut cover are not taken by the metal rod but by the fabric itself. This is manifested as a surface dimpling or dipping along the exposed seam where the tension loads are transmitted to the face side of the cover.